AVIAT NETWORKS MICROWAVE BACKHAUL FOR PUBLIC SAFETY LTE

Transcription

1 AVIAT NETWORKS MICROWAVE BACKHAUL FOR PUBLIC SAFETY LTE

2 INTRODUCTION THE EVOLUTION TO LONG TERM EVOLUTION Public safety agencies are soon to experience a dramatic improvement in communications capabilities enabled by advances in technology. New broadband multimedia applications will give first responders and commanders alike far better situational awareness, and thereby improve both the effectiveness and safety of all personnel charged with protecting the public. The specific technology, now mandated by the U.S. Federal Communications Commission (FCC) for all new emergency communications networks, is Long Term Evolution, or LTE a fourth-generation broadband solution. The FCC has also allocated licensed spectrum to ensure the best possible performance in these new networks. These FCC rulings support the goal of achieving an interoperable nationwide network for public safety agencies. The FCC chose LTE based on its proven ability to support voice, video and data communications at remarkably high data rates that were previously only possible with wired links. Although there will be some differences in a nationwide public safety network involving capacity and coexistence with Land-Mobile Radio communications, lessons learned from LTE s deployment in large-scale commercial mobile operator networks will help ensure achieving the FCC s goal cost-effectively. This white paper addresses one of the most important aspects of LTE networks: backhaul. As will be shown, microwave technology is particularly well suited to addressing the three main challenges involved in backhauling LTE traffic: capacity, reliability and cost. The paper also provides valuable recommendations based on current best practices, including those that maximize long-term flexibility and affordability. With the recent developments in both spectrum and funding allocations, it has become clear that LTE will be the future of public safety communications in North America, if not globally. LTE represents an unprecedented opportunity for better communications more applications, more tools, more real-time video and data ultimately arming first responders with more information and enabling them to be more capable, efficient, safe and secure. Not only is LTE a vast improvement over today s public safety voice-only communications technology, LTE offers three notable advances over the third-generation solutions now being used in commercial cellular networks. The first is remarkably high data rates up to 10 times faster than 3G. The second is an order of magnitude lower latency, which is important for supporting real-time applications. Third is LTE s relatively lower cost as a purely digital network. In addition, LTE also offers improved security, reliability, Quality of Service, management and interoperability that will be very important in public safety applications. Narrow band Land-Mobile Radio (LMR) communications have served public safety agencies well, but its lack of broadband data capabilities makes it unsuited to meet future communications needs. LMR has features purpose-built for public safety that are not yet supported today by LTE (such as mission-critical voice, direct mode communications, etc.), meaning both technologies will continue to be used in public safety networks well into the future. Moreover, as a next-generation technology, LTE is relatively new (even for mobile operators) so it will take time for public safety agencies to work through the issues that accompany this new technology. So, Long Term Evolution is just that: an evolution, over time, to more capable communications technology.

3 LTE BACKHAUL CHALLENGES When compared with LMR, LTE requires more bandwidth and more cell sites, making backhaul more complicated and more costly. Careful attention must be paid to backhaul design, therefore, to minimize cost and complexity. In addition, because public safety networks are mission-critical, reliability cannot be sacrificed to meet cost and capacity objectives. THE NEED FOR SPEED One challenge with LTE is satisfying the backhaul capacity needs and in order to determine the backhaul capacity required, it is first necessary to understand the capacity supported by the individual cellsites. With all wireless communications, signal strength diminishes with distance. LTE utilizes three modulation schemes - 64QAM (64-state Quadrature Amplitude Modulation), 16QAM (16-state QAM) and QPSK (Quadrature Phase Shift Keying) that produce maximum downstream throughputs of 43, 28 and 14 Megabits per second (Mbps), respectively, in the 10 MHz D-Block of the 700 MHz spectrum allocated by the FCC for exclusive use in public safety networks. Note that the lower upstream throughput rates of 14, 10 and 5 Mbps, respectively, have less of an effect on sizing backhaul capacity in the bi-directional, symmetrical links in the backbone ring. Because LTE cell sites have three sectors of 120 each, these throughputs are available on each sector. In addition, Multiple Input/Multiple Output (MIMO) technology with multiple radios (or streams) can double or even quadruple these data rates in 2x2 and 4x4 configurations, respectively. While a full analysis of these considerations is beyond the scope and intent of this paper, their conservative application to public safety networks yields a theoretical backhaul bandwidth requirement of 100 to 150 Mbps for an LTE cell site. It s important to note however that these rates are theoretical peak figures when one user, or even a few, are connected to the cell site. Even though such large bandwidths are not needed for a single user (based on application requirements) even in a public safety network, the backhaul planning scenario prescribes connectivity to multiple users. Nonetheless, capacity planning for IP networks is new to public safety and ultimately dependent on volume of traffic and QoS requirements of each application running on the network. For these reasons, and because traffic volumes, and QoS requirements have not been figured out, we expect the best practices for LTE backhaul capacity planning in public safety to be an evolving process. SINGLE USER DOWN/UP DATA RATE vs. DISTANCE FROM CELL CENTER Close Medium Far 5MHz Channel BW 10MHz Channel BW Public Safety (FDD) 17/5.6 Mbps 11/3.7 Mbps 5.6/1.8 Mbps 43/14.4 Mbps 28/9.5 Mbps 14/4.8 Mbps DOWNSTREAM/UPSTREAM DATA RATES FOR 5 MHZ AND 10 MHZ CHANNELS IN THE 700 MHZ SPECTRUM AVIAT NETWORKS 3

4 WHEN FAILURE IS NOT AN OPTION: THE NEED FOR HIGH RELIABILITY Public safety applications are mission-critical by definition. While reliability is often measured by uptime in mobile operator networks, any downtime of a base station is not an option. When in dangerous situations, first responders require secure and sustained communications and constant access to situational information. They must be able to locate, track and communicate with assets even during failover scenarios. These additional requirements involve robust security (e.g. rigorous user authentication and authorization, application access controls, strong link encryption, and intrusion detection and prevention), accurate network synchronization, and assured Quality of Service (QoS) to prioritize and shape the traffic for the most critical of users and applications. POTENTIAL FOR EXPLODING COSTS In LTE networks, there is an important factor affecting cost: increased number of cell sites. The shorter radius of an LTE cell (about 3 miles) compared to that for an LMR base station (about 20 miles, excluding line-of-site considerations), requires 3 to 5 times as many LTE cell sites to provide equivalent and complete coverage. Even though a LTE base station will cost much less than a LMR base station, deploying 3 to 5 times more LTE sites is expected to increase base station costs over an LMR configuration only slightly. The increase in the number of sites however means many more backhaul links (and higher capacity backhaul at that) are needed, creating much higher microwave costs. The cost comparison chart below indicates that the microwave backhaul component would be higher for LTE than LMR. Solutions will be needed to manage this cost challenge. In short, Public safety LTE networks need to be treated with the same mission-critical mentality as traditional LMR networks have been perhaps even more so because packet-based traffic can be less reliable and less secure than TDM traffic. Indeed, first responders will come to depend on LTE data just as much as they do on LMR voice today. In addition, despite being data-only initially, LTE networks will eventually also carry voice traffic. So the systems deployed today will need to support future capabilities with the same mission-critical reliability. INITIAL COST LTE LMR MICROWAVE BACKHAUL COMPONENT BASE STATION COMPONENT COST FOR EQUIVALENT COVERAGE AREA, WITH FIVE LTE SITES PER LMR SITE 4 AVIAT NETWORKS

5 MICROWAVE BACKHAUL FOR LTE NETWORKS All three challenges are readily addressed with a carrierclass microwave backhaul network solution. This solution also provide the versatility and extensibility needed to accommodate future changes in public safety LTE networks, including the eventual migration to a purely packet-based configuration for all voice, video and data communications. CAPACITY Advances in microwave technology, more spectral efficiency (from a combination of higher modulation rates and data optimization) together with more backhaul spectrum (with link aggregation over multiple channels), can support up to 1 Gigabit per second (Gbps) per link far more than is needed for LTE backhaul. Because of increased microwave capacity capabilities, the capacity bottleneck is now focused on the LTE access network itself. This will remain true regardless of the outcome of a Public Safety Communications Research study on the acceptable overbooking factors, meaning that the 1 Gbps capacity of microwave backhaul links is more than sufficient to handle the throughput requirements of even the largest public safety networks. RELIABILITY LTE backhaul networks need to be designed with the same or better network reliability and availability as LMR networks. In addition to the customary methods for providing high reliability (e.g. a resilient ring topology, equipment redundancy with 1+1 protection, Forward Error Correction, and traffic shaping and prioritization), here are some of the other characteristics of today s missioncritical microwave solutions: Hybrid radios The ability to handle both TDM and IP traffic in their native modes is critical to ensuring efficient and dependable operation of the converged LMR and LTE services over the same infrastructure. most serviceable, thereby providing a combination of the lowest mean time between failures (MTBF) and fastest mean time to repair (MTTR). Security With the evolution to packet-based applications, security is important and should, therefore, be built into the microwave backhaul system with features like payload encryption and comprehensive management security provisions. High Performance To ensure the most reliable path designs, highest capacity and lowest cost, radio system gain becomes a critical criterion when choosing a microwave solution. In light of minimizing antenna costs and ongoing operational expenditures, high system gain is even more critical in LTE networks. Platform redundancy Despite the resiliency inherent in the LTE backbone ring topology, individual systems should still possess fully-redundant, protected configurations at the port, card and system levels.. AFFORDABILITY In microwave backhaul networks, the five-year total cost of ownership (TCO) is overwhelming weighted toward ongoing operational expenditures (OpEx), at >80%, compared to capital expenditures (CapEx), at < 20%, as shown in the diagram below. Minimizing TCO, therefore, requires paying particular attention to the OpEx. 5% 12% 54% 29% All-indoor radios In addition to offering the lowest total cost of ownership in high capacity deployments (covered below), all-indoor radios are also the most reliable and Total Initial OPEX Total Ongoing OPEX Total Initial CAPEX Total Ongoing CAPEX AVIAT NETWORKS 5

6 To minimize OpEx, there are four proven practices that apply to public safety LTE networks: Reuse existing infrastructure where possible, overlay where necessary. Leveraging existing infrastructure is always a prudent practice and this especially true when endeavoring to minimize costs in a hybrid LMR/LTE public safety network. With the right solution it is possible to utilize the towers, antenna, cabling, management systems and any available expansion ports, at all existing LMR sites. The most costeffective way to do this is with all-indoor radios (covered in more detail below, left). Where reuse of the antenna is impractical or impossible, an overlay with a split-mount radio is also a cost-effective approach. Both the reuse and overlay configurations are shown in the diagram. Given that the LMR and LTE networks will need to coexist for the foreseeable future, until LMR can be replaced completely by Voice over IP (VoIP) technology, a hybrid TDM/IP radio provides maximum migration flexibility. Use all-indoor radios in the backbone ring(s) The use of all-indoor radios in the backhaul network normally results in a lower TCO despite the slightly higher initial CapEx. There are no antennas to purchase and install, and no need to even climb the tower to grow the capacity. As a result, the deployment and ongoing maintenance are dramatically simplified. An available waveguide expansion port on all-indoor radios will enable the new radio to easily connect to the existing waveguide cabling with negligible interruption to the existing system, enabling capacity to be increased as needed. COST COMPARISON BETWEEN RE-USE AND FULL OVERLAY CONFIGURATIONS Use Hybrid TDM/IP radios for maximum migration flexibility The reuse of existing LMR sites raises an important design choice between hybrid TDM/IP (Internet Protocol) and all-ip backhaul. Hybrid solutions carry TDM (voice) and IP (data and digital video) traffic in their native modes. An all-ip solution must somehow accommodate TDM traffic. One common way to do this is with pseudowire. Pseudowire emulates TDM links over IP networks, but adds complexity, additional overhead and latency, and can create synchronization and other problems for the voice traffic. These risks may be too great for the modest potential savings in CapEx especially given the likely increase in OpEx due to the increased complexity. Use split-mount or all-outdoor radios for low-cost spur sites The likely topology for a hybrid LMR/LTE public safety network, is a core ring comprised of a mix of existing LMR and new LTE sites, with spurs to the additional LTE sites required for coverage. Note that because the spur sites are not on the resilient ring, these links may require a fully redundant configuration with protection provisions to achieve mission-critical reliability. For new sites, more cost-effective split-mount or all-outdoor radios can be used. 6 AVIAT NETWORKS

7 NEW LTE spur site LMR + LTE LMR + LTE site LMR + LTE NEW LTE spur site LMR + LTE LMR + LTE site LMR + LTE NEW LTE spur site PUBLIC SAFETY LTE NETWORK WITH A CORE RING AND SPUR SITES CONCLUSION The new broadband multimedia public safety applications enabled by LTE will give first responders and commanders alike greater situational awareness with capabilities like live video feeds, coordinated multi-agency incident command and control, and access to aerial imagery, GIS mapping, and local, state and national databases. These and other new capabilities will coexist with LMR voice communications for the foreseeable future, enabling a gradual transition to a converged LTE network that will eventually support all voice, video and data communications. Challenges remain, however, particularly with the need to deploy many more LTE cell sites owing to its shorter range compared with LMR communications. The LTE network must also have the capacity and the reliability required for public safety applications. The most versatile and costeffective way to satisfy these demanding requirements for coverage, capacity and reliability is wireless microwave. For supporting link capacities of 1 Gbps or more, microwave backhaul has more than ample capacity to support LTE networks for the foreseeable future, and the technology has proven its reliability in commercial carrier networks designed for % uptime. The real challenge for public safety agencies is to make the new LTE network as affordable as possible. Aviat Networks has industry-leading expertise in the design, deployment and maintenance of missioncritical microwave backhaul systems that enable the migration to the LTE broadband future. With more than 750,000 systems installed around the world, Aviat Networks has built a reputation as a leader in offering the most cost-effective solutions for public and private telecommunications operators worldwide. To learn more about how Aviat Networks can provide mission-critical affordability for your public safety LTE network, visit us at AVIAT NETWORKS 7

8 Aviat, Aviat Networks, and the Aviat logo are trademarks or registered trademarks of Aviat Networks, Inc. Eclipse is a trademark of Aviat U.S., Inc. Aviat Networks, Inc. (2012) All Rights Reserved. Data subject to change without notice. _wp_publicsafetylte_22jun12